|
(11) | EP 2 160 853 B1 |
| (12) | EUROPEAN PATENT SPECIFICATION |
|
|
| (54) |
ADAPTIVE ANTENNA TRANSMISSION ADAPTIVE ANTENNENÜBERTRAGUNG EMISSION D'ANTENNE ADAPTATIVE |
|
|
||||||||||||||||||||||||||||
| Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention). |
Technical field
[0001] The present invention relates to a method for adaptive antenna transmission and a method for antenna calibration.
Background
[0002] It is well known that adapting transmission parameters to the current channel conditions improves the performance of a wireless communication system. Parameters that can be adapted are for example the power allocation, both in the frequency domain and on different antennas in a multi antenna system, as well as modulation, coding, etc.
[0003] With channel state information (CSI) at the transmitter it is possible to allocate the available power to the parts of the frequency spectrum that have good channel conditions, i.e. not waste the power on frequencies that are in deep fade for the moment. On the parts of the spectrum that have good channel conditions it is also advantageous to use higher order modulation and lower coding rate.
[0004] In future mobile systems larger bandwidths will be used and therefore broadband antennas. The gain of these broadband antennas are however not equal over the whole frequency range. In a handheld unit the gain on different frequencies will also change when the antenna interacts with the user. In a system where the CSI is reported by a receiving unit to a transmitting unit, the antenna gain will be incorporated in the reported CSI.
[0005] In systems with multiple transmit antennas it is also known that the capacity of the system is improved when the transmission parameters are adapted to the current channel conditions for each antenna. Once again not to waste power on an antenna that is in a deep fade or for some other reason have poor channel conditions.
[0006] An optimal power allocation can only be achieved when the transmitter has full CSI. Without CSI at the transmitter it is not possible to adapt to the current channel conditions at the transmitter and the best strategy is to transmit equal power, same modulation format and same coding rate over the whole frequency band and at all antennas, as illustrated in figure 5.
Summary
[0007] An object of the present invention is to provide a method to adapt the transmission parameters of a transmitter without the need to obtain information regarding the channel condition.
[0008] By measuring the reflection coefficient(s) at the transmitter the relative antenna gain can be estimated on different frequencies and/or different antennas if more than one antenna is provided. It is then possible to adapt the transmission parameters without any CSI at the transmitter based on this frequency/antenna dependent reflection coefficient.
[0009] When measuring the reflection coefficient it is also possible to measure the propagation time from the antenna port to the actual antenna, i.e. the delay introduced by antenna feeders etc. In a system with multiple antennas it is then possible to compensate for the different time delay in the different transmitter chains, assuring that the signal is transmitted simultaneously from all antennas. It is possible to ensure that the signals will be transmitted with a known amplitude and phase. This is often called antenna calibration.
[0010] An advantage with the present invention is that an improved performance of a wireless communication system is obtained compared to not adapting power allocation, modulation format, coding rate etc., although the adaptation is not optimal.
[0011] Another advantage with the present invention is that the interaction between a user and a handheld mobile unit are taken into consideration, thus providing an improved performance.
[0012] Additional objects and advantages will become apparent for the skilled person from the detailed description of the preferred embodiments.
Brief description of the drawings
[0013]
Fig. 1 shows an illustration of a communication channel.
Fig. 2 shows the transmitter chain of the communication channel provided with a first embodiment of the invention implemented in the transmitter chain.
Fig. 3 shows a communication channel provided with a second embodiment of the invention implemented in the receiver chain.
Fig. 4 shows a plot of measured reflection coefficients used in the present invention.
Fig. 5 shows a graph illustrating uniform power allocation in an OFDM system according to prior art.
Figs. 6a - 6c show graphs illustrating power allocation in an OFDM system according to the present invention.
Fig. 7a shows the transmitter chain of the communication channel provided with a third embodiment of the invention implemented in the transmitter chain.
Fig. 7b shows a graph illustrating power allocation between transmit antennas for the transmitter chain in figure 7a.
Figs. 8a and 8b show allocation of power for each transmit antenna in figure 7a as a function of frequency.
Fig. 9a shows the transmitter chain of the communication channel provided with a fourth embodiment of the invention implemented in the transmitter chain.
Fig. 9b shows a graph illustrating power allocation between antennas elements for the transmit antenna in figure 9a.
Fig. 10 shows a telecommunication system according to the present invention.
Fig. 11 shows a communication channel provided with a fifth embodiment of the invention implemented in the receiver chain and in the transmitter chain.
Detailed description
[0014] Figure 1 shows the different parts of a communication channel 10 interconnecting a signal source 11 and devices, such as speaker, display memory, etc. in a receiving unit 12. The communication channel 10 comprises the transmitter chain 13, the wireless radio channel 14, and the receiver chain 15. The transmitter chain 13 comprises in this example a transmitter Tx, a transmit distribution network 16 and three transmit antennas 17, each having one or more antenna elements (not shown). The receiver chain 15 comprises in this example two receive antennas 18, a receive distribution network 19 and a receiver Rx, which comprises means to process received data and forward information to the devices in the receiving unit 12.
[0015] Each transmit antenna 17 is connected to the signal source 11 via an individual transmitter chain including the transmitter Tx and a part of the transmit distribution network 16. Each receive antenna 18 is connected to the receiver Rx via an individual receive chain including the receiver Rx and a part of the receive distribution network 19.
[0016] Traditionally, information regarding the channel condition has been determined by the receiver unit and reported back to the transmitter as indicated by the dashed line denoted CSI. The CSI includes information regarding the complete communication channel, whereby the transmitter Tx adapts the transmission parameters based on the CSI.
[0017] If the transmitter chain 13 comprises multiple transmit antennas 17 and employs beam forming, or some other form of precoding, it may also be necessary to have calibrated antennas, i.e. adjust the individual transmitter chain to make sure that the signal is transmitted from the transmit antennas simultaneously and with known amplitude and phase. This is normally achieved by requesting calibration measurements reports from user equipment communicating through the transmit antennas, and thereafter estimating parameters to compensate for the RF chain impairments, as described in reference [1] and [2].
[0018] Figure 2 shows a transmitter chain 20 of a communication channel provided with a first embodiment of an adaptation circuit 21. The transmitter chain 20 is provided with a transmitter Tx connected to a signal source 11, and a distribution network 26 connected to the transmitter Tx and an antenna port of one transmit antenna 27 having five antenna elements 22 arranged on an antenna panel 23. A beam forming network 24, which is integrated in the antenna 27, is supplied with a signal from the transmitter Tx, and is connected to each antenna element 22. The beam forming network 24 may comprise phase shifters and means to adapt the amplitude of the signal being fed to each antenna element 22. A directional coupler 25 is used to determine the reflection coefficient together with the adaptation circuit 21, which preferably comprises a receiver capable of comparing the transmitted reference signal with the reflection of the same signal - thereby calculating S11. A system for determining the reflection coefficient is described in reference [3]. The reference signal could either be the ordinary transmission from the transmitter Tx, or a signal generated in the adaptation circuit and transmitted from the transmitter during idle periods of the transmitter
[0019] The inventive concept relies on the ability to measure the reflection coefficient, usually denoted S11, of a signal at each antenna using the adaptation circuit 21. S11 is in this embodiment measured as a function of frequency, i.e. S11(f), and the relative antenna gain can be estimated on different frequencies based on the reflection coefficient. It is then possible to adapt the transmission parameters, without the feedback of channel state information CSI, at the transmitter based on the measured frequency dependent reflection coefficient. Only the characteristics of the Tx chain 20 will be taken into consideration when adapting the transmission properties, which will result in a sub-optimal adaptation compared to the prior art adaptation with CSI. However, the sub-optimal improvement will still provide an improvement compared to not adapting power allocation, modulation format, coding rate, etc.
[0020] The reflection coefficient S11(f) is a measure of how much of the transmitted power that is reflected by the antenna (and other parts of the transmission chain). The power that is not reflected can be assumed to be transmitted by the antenna. Some parts will be burnt in the internal load of the antenna but the fraction of energy lost in the internal load is often small and does not have a frequency-dependence, or a very slight frequency-dependence, and will therefore not affect the optimal power allocation vs. frequency. The part of the transmit power that actually is transmitted, i.e. the transfer function, H(f) can thus be expressed as:
[0021] If S11(f) is measured at the transmitter for the Tx chain, as illustrated in figure 2, a sub-optimal power allocation can be calculated without any CSI at the transmitter by performing "water filling", as described in more detail below. The reflection coefficient S11 may also be measured for the Rx chain in a similar fashion, as illustrated in connection with figure 3. In the following illustrative examples, the reflection coefficient for the TX chain
(continuous thin line in figure 4) and the relative coefficient for the Rx chain
(dotted line in figure 4) have been measured, and the corresponding transfer functions Htx and Hrx, respectively, have been calculated using equation (1) and used to illustrate the inventive concept.
[0022] Figure 3 shows a receiver chain 30 of a communication channel provided with an adaptation circuit 31. The receiver chain 30 is provided with a receiver Rx connected to devices in a receiving unit 42, and a distribution network 39 connected to the receiver Rx and an antenna port of one receive antenna 38 having three antenna elements 32. A signal transmitted from the transmitter Tx is received by the antenna elements 32 and forwarded to the receiver Rx through the distribution network 39. A directional coupler 33 is used to determine the reflection coefficient together with the adaptation circuit 31, which preferably comprises a receiver capable of comparing the transmitted reference signal with the reflection of the same signal - thereby calculating S11, see reference [3]. The adaptation circuit 31 generates a weak signal which is transmitted to the receiver antenna 38 and is reflected by the antenna elements 32 of the receive antenna 38, and the reflection coefficient may be determined. The weak signal generated by the adaptation circuit 31 is preferably selected to be transmitted when the receiver Rx is not receiving any signals from the transmitter Tx, or the magnitude of the weak signal is much lower than the magnitude of the received signal to avoid distortion of the received signal and/or interference towards other units communicating on the same frequencies. In a time-division duplex (TDD) unit, measurements of the reflection coefficient(s) may be done during the time slot at which the unit is transmitting provided the receiver chain and transmitter chain are calibrated. The unit could then make use of the transmitted data as reference without the need for a special reference signal to be transmitted. The adaptation circuit 31 is, in this embodiment, arranged in the receiver unit 42, such as a base station or a mobile unit, and information regarding channel condition is signaled to the transmitter Tx in order to adapt the transmission parameters accordingly. This signaling would typically require much less frequent signaling compared to full CSI feedback.
[0023] The arrangement to measure the antenna reflection coefficient(s) at the receiving unit may be useful in the case that the receiver should signal its preference for e.g. a certain frequency band (subcarrier allocation in OFDM) but does not yet have any received data upon which it can estimate the channel conditions. Such a situation could occur e.g. during random access or when pilot symbols are not transmitted across the entire available frequency band. By measuring the reflection coefficients at the receiver, the receiving unit can predict what frequencies that would be more likely to support good channel conditions. Most importantly, the use of frequencies where the receiving antenna currently is poorly matched can be avoided.
[0024] The invention will be illustrated using an OFDM (Orthogonal Frequency Division Muliplex) system since the system operates in the frequency domain. However, the invention is not limited to OFDM system and may be implemented in other telecommunication systems, such as WCDMA.
[0025] Figure 4 shows a plot of reflection coefficients S11 in relative power [dB] as a function of subcarrier index [n] of an OFDM system. A measured reflection coefficient
for a transmitter chain as described in connection with figure 2 is illustrated by a thin continuous line, and a measured reflection coefficient
for a receiver chain as described in connection with figure 3 is illustrated by a dotted line. A calculated combined reflection coefficient
is also indicated by a fat continuous line. The Relative power in figure 4 is in relation to transmitted power from the transmitter for
and in relation to incoming power to the receiver antenna for
[0026] Figure 5 shows a power allocation graph illustrating transmission parameter adaptations for an OFDM system having 64 sub-carriers, wherein each bar represents a sub-carrier. The solid part of each bar represents the inverted transfer function of both the transmitter chain and the receiver chain (Htx ∗ Hrx)-1. Note that the transfer function of the radio channel is omitted. A uniform power distribution has been applied according to prior art, as mentioned above. The uniform power allocation is illustrated as Tx power in the graph on top of the solid part of each bar.
[0027] As an example, the power allocation on subcarrier n in an OFDM system with the known transmission function H(f) can be calculated as:
where λ is chosen such that
where Ptot is the total transmit power of the transmitter Tx and N is the number of subcarriers of the OFDM system. An illustration of the waterfilling concept is presented in figures 6a-6c.
[0028] Figure 6a shows a graph illustrating power allocation in an OFDM system according to the present invention, wherein the transfer function of the transmitter chain Htx and the transfer function of the receiver chain Hrx are both known to an adaptation circuit, such as the system described in connection with figure 11.
[0029] The solid parts of each bar represent the inverted transfer function of both the transmitter chain and the receiver chain (Htx ∗ Hrx)-1 as described in connection with figure 5. "Waterfilling" has been applied to allocate Tx power to the sub-carriers n. The frequencies represented in the sub-carriers arranged between 28 and 38 are predicted to have the best conditions for the transmission, and thus most transmit power has been allocated to these sub-carriers. Frequencies represented in sub-carriers arranged below 10 and above 55 are predicted to have the worst conditions for the transmission, and therefore no transmit power has been allocated to these sub-carriers.
[0030] If the transfer function of the receiver chain is not known, an adaptation based on the transmitter chain may be performed. Figure 6b shows a graph illustrating power allocation in an OFDM system according to the present invention, wherein only the transfer function of the transmitter chain Htx is known to an adaptation circuit, such as the system described in connection with figure 2.
[0031] The solid parts of each bar represent the inverted transfer function of the transmitter chain (Htx)-1. "Waterfilling" has been applied to allocate Tx power to the sub-carriers n based on only the transmitter transfer function. The frequencies represented in the sub-carriers arranged between 33 and 41 are predicted to have the best conditions for the transmission, and thus most transmit power has been allocated to these sub-carriers. Frequencies represented in sub-carriers arranged below 14 and above 59 are predicted to have the worst conditions for the transmission, and therefore no (or very little) transmit power has been allocated to these sub-carriers.
[0032] Figure 6c illustrates the impact of the transmit power allocation determined in figure 6b, based on the transfer function of the transmitter chain, in relation to the inverted transfer function of both the transmitter chain and the receiver chain (Htx ∗ Hrx)-1. A comparison between the prior art power distribution presented in figure 5 and figure 6c indicate that a major part of the available transmit power in the transmitter is allocated to sub-carriers having low reflection coefficients. However, it should be noted that the power allocation is not as good as the power allocation illustrated in figure 6a, since knowledge of the receiver reflection coefficient(s) will provide an even more improved power allocation compared to prior art (figure 5).
[0033] For systems with multiple transmit antennas the average transmit coefficient can be calculated for each transmit antenna. This mean value can then be used to perform waterfilling across the transmit antennas provided a first data stream is supported over a first antenna and orthogonal to a second data stream on a second antenna or for example choose which antenna to transmit on if transmit selection diversity is used. As an example the mean transfer function for transmit antenna number one Htx1 in an OFDM system can be calculated as
[0034] If S11 is not measured as a function of frequency but rather as the mean value over the whole frequency band this part of the invention is still applicable.
[0035] Fig. 7a shows a transmitter chain 40 of the communication channel provided with a third embodiment of the invention implemented in the transmitter chain. Antenna ports of two transmit antennas 471 and 472, each having a single antenna element 22 are connected to a transmitter Tx using a distribution network. A signal source 11 is connected to the transmitter Tx and directional couplers 45 are used to determine a reflection coefficient together with an adaptation circuit 41 for each transmit antenna 471 and 472 (commonly denoted as 47). The adaptation circuit 41 calculates, or measures, in this embodiment the mean value of the reflection coefficient for each antenna as mentioned above. This results in a calculated mean transfer function for each antenna. Information regarding the reflection coefficients and/or transfer functions are used to control the transmitter Tx to generate the desired transmit power allocation.
[0036] Fig. 7b shows a graph illustrating power allocation between transmit antennas 471 and 472 for the transmitter chain 40 in figure 7a. The inverse mean transfer function for each antenna is illustrated by the solid part of the bars, and waterfilling over the antennas results in the power allocation as indicated provided the datastream on each antenna is orthogonal against each other. The major portion of the transmit power is directed to antenna 2.
[0037] It should be noted that the adaptation circuit could be provided with means to select which antenna to transmit on in dependency of the measured reflection coefficient. In this example, antenna 2 should be selected and antenna 1 is not used until the measured reflection coefficients for the antennas indicate better transmission properties for antenna 1.
[0038] If the reflection coefficient for each antenna in figure 7a is measured as a function of frequency, the mean transfer function is calculated using equation (4). The power allocated to each antenna (as indicated in figure 7b) may be allocated across the frequency range for each antenna. This is illustrated in figures 8a and 8b, which show allocation of power for each transmit antenna in figure 7a as a function of frequency. Waterfilling across the frequency is used in combination with waterfilling across the antennas.
[0039] Fig. 9a shows a transmitter chain 50 of the communication channel provided with a fourth embodiment of the invention implemented in the transmitter chain. A transmitter Tx, connected to a signal source 11 supply signals to three antenna ports of an antenna 57 comprising three antenna elements 521, 522, 523, commonly denoted 52, each connected to one of the three antenna ports. A directional coupler 55 is used to determine the reflection coefficient for each antenna element together with an adaptation circuit 51. The adaptation circuit 51 measures the reflection coefficient for each antenna element 52, either as a mean value or as a function of frequency, and calculates a transfer function for each antenna element. Information regarding reflection coefficient and/or transfer function is used to control the transmitter Tx to adapt the transmission parameters, such as allocate the transmit power.
[0040] Fig. 9b shows a graph illustrating power allocation between antennas elements 52 for the transmit antenna 57 in figure 9a. Waterfilling across the antenna elements has been applied, but it is naturally possible to select only one or two of the antenna elements to transmit the signal from the signal source.
[0041] Fig. 10 shows a telecommunication system according to the present invention. A base station 60 including an antenna tower 61 provided with a base station antenna arrangement 62, and base station equipment BSE, which includes transmitter, receiver, and adaptation circuit as described in the preferred embodiments. A mobile unit 63 is within the coverage area of the base station and communicates with the BSE via the base station antenna arrangement 62 as indicated by 64. Furthermore, an optional signal 65 may be transmitted from the mobile unit 63 to the BSE if the mobile unit is equipped with the resources to measure the reflection coefficient of the receive chain as described in connection with figures 3 and 11.
[0042] Fig. 11 shows a communication channel provided with a fifth embodiment of the invention implemented in the transmitter chain 70 and in the receiver chain 80.
[0043] The transmitter chain 70 comprises in this embodiment a transmitter Tx, connected to a signal source 11, and feeding signals to antenna ports of two antennas 771 and 772 (commonly denoted 77) through a distribution network 76. Each antenna is provided with five antenna elements 22. Directional couplers 751 and 752 are used together with an adaptation circuit 71 to determine the reflection coefficient S11 for each antenna 771, 772, each having an individual transmit chain. The adaptation circuit 71 may be configured to calculate a signal indicative of suitable transmit power allocation, beamforming weights, modulation, coding, etc which is forwarded to the transmitter, as indicated by connection 72 based on the determined reflection coefficient for the transmit chain 70 and the determined reflection coefficient for the receive chain 80.
[0044] The receiver chain 80 comprises in this embodiment a receiver Rx that receives signals from antenna ports of two receive antennas 881 and 882 (commonly denoted 88) through a distribution network 89. Each antenna is provided with three antenna elements 22. Directional couplers 831 and 832 are used together with a circuit 81 to determine the reflection coefficient(s) for each receiver chain. The circuit may be configured to calculate the transfer function(s) Hrx based on the determined reflection coefficient(s) and thereafter transmit information regarding channel condition back to the adaptation circuit 71 in a suitable way, e.g. wireless signaling over the radio channel. The receiver is connected to devices in a receiving unit 92.
[0045] As an example, the effect of waterfilling of the available transmit power is illustrated in connection with figure 6a as described earlier. Other types of suitable transmit power allocation, beamforming weights, antenna selection, modulation and coding may be performed as a result of the calculated transfer function for both the transmitter chain 70 and the receiver chain 80.
[0046] The transmitter chain described in connection with figures 2, 7a, 9a and 11 may be implemented in a base station and/or a mobile unit in a communication system as illustrated in connection with figure 10. The receiver chain described in connection with figures 3 and 11 may also be implemented in a base station and/or a mobile unit in a communication system as illustrated in connection with figure 10.
[0047] The needed update rate for the S11 measurements is different for a mobile unit and a base station. At the base station S11 is not likely changed at a high rate and therefore the measurements can be updated at a slow rate. This is because the connections to the antenna and the environment around the antenna are almost static. At the mobile unit, on the other hand, S11 change rather fast as the user interacts with the antenna. Therefore S11 measurements have to be updated at a higher rate. A typical update rate at the mobile unit is once per second, or higher.
Calibration
[0048] In a system with multiple transmit antennas, such as described in connection with figures 7a and 11, it is possible to perform antenna calibration with or without the adaptation of the transmission parameters based on the measured reflection coefficient S11 as described earlier. The antenna calibration is performed by compensating for the different time delay in the available transmitter chains, in order to assure that the signal is transmitted simultaneously from all antennas, and also to ensure that the amplitude and the phase on each antenna is equal or at least known. If the system employs beamforming or some other form of precoding it is sometimes necessary to have calibrated antennas. The present invention provides means to perform antenna calibration without any feedback from the receiver.
[0049] The different time delays are determined by measuring the propagation time from the antenna port to the actual antenna, i.e. the delay introduced by antenna feeders etc. This time delay may be deduced from the S11(f) measure by e.g. performing an inverse Fourier transform of S11(f) giving an equivalent impulse response s11(τ). The time delay τpeak is visible as a peak in s11(τ) that will correspond to the propagation delay from the transmitter Tx to the reflection point at the antenna and back to the adaptation circuit 71. From this delay the time delay from the transmitter to the antenna may be determined by dividing τpeak by 2. The measurement is performed on the individual transmitter chain for each antenna, as described in more detail below.
[0050] In figure 7a, each transmit antenna 471 and 472 receives a signal from the transmitter Tx via an individual transmitter chain 481 and 482, respectively. The adaptation circuit 41 may be configured to only measure the propagation time for each transmitter chain 481 and 482, or it may be configured to measure the propagation time together with the functionality to determine the reflection coefficients of each transmit antenna 471 and 472.
[0051] In figure 11, each transmit antenna 771 and 772 receives a signal from the transmitter Tx via an individual transmitter chain 781 and 782, respectively. The adaptation circuit 71 may be configured to only measure the propagation time for each transmitter chain 781 and 782, and also be configured to receive information regarding reflection coefficient(s) and/or channel condition from the circuit 81 in the receiver chain 80 to adapt the transmission parameters only based on the determined transfer function Hrx of the receiver chain. However, it is also possible to configure the adaptation circuit 71 to measure the propagation time together with the functionality to determine the reflection coefficients of each transmit antenna 771 and 772.
[0052] The main advantage of the invention is the possibility to adapt the transmission parameters, such as antenna selection, power allocation, beamforming weights, modulation and coding rate, without any CSI at the transmitter. The adaptation will be suboptimal but nevertheless provide an improvement over the traditional equal power/modulation/coding rate allocation. In a handheld unit the antenna gain on different antennas and on different frequencies will change as the user interacts with the antennas. With this invention these effects are taken into consideration in the waterfilling solution.
[0053] For systems with multiple transmit antennas it is possible to adapt the transmission parameters across the transmit antennas without CSI at the transmitter. This is particularly useful at the mobile station since one can avoid transmitting on an antenna that is attenuated by the user. As the interaction between a user and the mobile station antenna easily can result in more than 10dB attenuation significant gains can be achieved.
[0054] If the transfer function of the receive chain is not available to the adaptation circuit in the transmitter unit when transmission parameters are adapted, a default transfer function
of the receive chain may be used in combination with the transfer function Htx of the transmitter chain. The default transfer function is preferably stored in the adaptation circuit and is preferably established based on a number of measured reflection coefficients from standard receiver units. This is most useful when the variations in reflection characteristics among different units are expected to be limited.
[0055] It is even possible to implement the present invention in a system using CSI to adapt the transmission parameters. The information regarding the transfer function of the transmitter chain may be used in the time period between the updated CSI is received by the transmitter unit since the changes of the transfer function in the transmitter normally are faster than the CSI has a possibility to forward to the transmitter.
[0056] The described embodiments have illustrated the invention to emphasize certain aspects, and it should be noted that it is obvious for a skilled person in the art to combine them to obtain a desired functionality.
[0057] The relative power used on the y-axis in figures 5, 6a-6c, 7b, 8a-8b, and 9b should be considered to be in relation to a fictitious power level used to illustrate the relative power levels between sub-carriers, antennas, or frequencies.
Abbreviations
[0058]
- CSI
- Channel State Information
- Htx, Hrx
- Transfer function for Tx chain and Rx chain
- OFDM
- Orthogonal Frequency Division Multiplex
- Rx
- Receiver
- S11
- Reflection Coefficient
- Tx
- Transmitter
- WCDMA
- Wideband Code Division Multiple Access
References
[0059]
- 1 3GGP R1-071048, "The Need for Measurement Report Mechanism Supporting NodeB RF Front End Calibration", Ericsson.
- 2. 3GGP R1-071602, "Absence of Array Calibration - Impact on Precoding Performance", Ericsson.
- 3. Agilent AN 1287-2, "Exploring the Architectures of Network Analyzers", Agilent Technologies.
1. A method for adapting transmission parameters in a transmitter (Tx) in communication with at least one antenna (27; 38; 47; 57; 77, 88), said method
comprising:
- transmitting a signal from the transmitter (Tx),
characterized in that said method further comprises:- determining at least one reflection coefficient (S11) of said signal for each antenna (27; 38; 47; 57; 77, 88) by comparing the transmitted signal with a reflection of the same signal, which at least one reflection coefficient (S11) is a measure of the transmitted power reflected by each antenna (27; 38; 47; 57; 77, 88), and
- adapting the transmission parameters based on the determined reflection coefficient (S11) wherein the transmission parameters comprises power allocation among carriers, beamforming weights, modulation and/or coding.
2. The method according to claim 1, wherein said reflection coefficient is determined
as a function of frequency.
3. The method according claim 2, wherein the at least one antenna is selected to be at
least one transmit antenna (27; 47; 57; 77) to which said transmitter (Tx) is connected, said reflection coefficient is determined for each transmit antenna
(27; 47; 57; 77) and the adaptation of transmission parameters comprises waterfilling
across the at least one transmit antenna (27; 47; 57; 77) to calculate power allocation
in frequency.
4. The method according to any of claims 1-3, wherein the at least one antenna is selected
to be multiple transmit antennas (47; 77) to which said transmitter (Tx) is connected, and said reflection coefficient for each transmit antenna (47; 77)
is determined as an average value over a frequency band.
5. The method according to claim 4, wherein each transmit antenna having one or more
antenna elements (22), the average value is calculated from the reflection coefficients
(S11) determined for each antenna element (22).
6. The method according to claim 4, wherein the average value is measured for each transmit
antenna (47).
7. The method according to any of claims 4-6, wherein the adaptation of transmission
parameters comprises waterfilling across the transmit antennas (47).
8. The method according to any of claims 3-6, wherein transmit selection diversity is
used and the adaptation of the transmission parameters comprises choosing which transmit
antenna (47) to transmit on.
9. The method according to claim 2, wherein the at least one antenna is selected to be
at least one receive antenna (38; 88) in a receiving unit (42; 92), said method further
comprises:
- determining at least one reflection coefficient (S11) of a weak signal transmitted to the at least one receiver antenna (38; 88) by comparing the transmitted weak signal with a reflection of the same weak signal in the receiving unit (42; 92),
- predicting channel conditions from the transmitter to the receiver based on the determined reflection coefficient(s) in the receiving unit (42; 92), and
- signaling information regarding reflection coefficients to the transmitter (Tx) in order to adapt the transmission parameters.
10. The method according to claim 9, wherein said information regarding channel conditions
comprises frequencies suitable for transmission and/or frequencies unsuitable for
transmission.
11. The method according to any of claims 9 or 10, wherein the reflection coefficient(s)
is/are determined relative the weak signal generated in an adaptation unit (31; 81)
in the receiving unit (42; 92) and transmitted to the receive antenna (38; 88).
12. The method according to any of claims 9 or 10, wherein the receiver unit is a time-division
duplex (TDD) unit, and the reflection coefficient(s) is/are determined during a time
slot at which the TDD unit is transmitting.
13. The method according to any of claims 1-8, wherein the at least one antenna is selected
to be multiple transmit antennas (47; 77) to which said transmitter (Tx) is connected, said method further comprises:
- determining a time delay based on reflection of the signal transmitted from the transmitter (Tx) for each individual transmitter chain (481, 482; 781, 782), and
- compensating for differences in time delay between the individual transmitter chains (481, 482; 781, 782) to assure that the signal is transmitted simultaneously from all transmit antennas (47; 77).
14. The method according to claim 13, wherein the time delay for each individual transmitter
chain (481, 482; 781, 782) is obtained by:
- measuring propagation time in each individual transmitter chain (481, 482; 781, 782) from antenna port in the transmitter (Tx) to each transmit antenna (47; 77), and
- calculating time delay to compensate for differences in time delay between the individual transmitter chains (481, 482; 781, 782).
15. The method according to any of claims 1-14, wherein said method further comprises
updating the measured reflection coefficient(s) at regular intervals.
16. The method according to claim 15, wherein the updating rate is higher when said transmitter
(Tx) and said at least one antenna are arranged in a mobile unit compared to when arranged
in a base station.
17. The method according to claim 16, wherein the updating rate is once per second, or
higher, for a mobile unit.
18. A node comprising at least one antenna, said node being configured to determine at
least one reflection coefficient of a signal for each antenna, said signal being transmitted
from a transmitter (Tx), characterized i n that said node further is provided with a means (21; 31; 41; 51; 71) to adapt in
said transmitter (Tx) based on the at least one reflection coefficient (S11) determined by comparing the transmitted signal with a reflection of the same signal,
which at least one reflection coefficient (S11) is a measure of the transmitted power reflected by each antenna, wherein the transmission
parameters comprises power allocation among carriers, beamforming weights, modulation
and/or coding..
1. Verfahren zum Einstellen von Sendeparametern in einem Sender (Tx), der in Verbindung mit zumindest einer Antenne (27; 38; 47; 57; 77, 88) steht, wobei
das Verfahren Folgendes umfasst:
- Senden eines Signals von dem Sender (Tx), dadurch gekennzeichnet, dass das Verfahren ferner Folgendes umfasst:
- Bestimmen von zumindest einem Reflektionskoeffizienten (S11) des Signals für jede Antenne (27; 38; 47; 57; 77, 88) durch Vergleichen des gesendeten Signals mit einer Reflektion desselben Signals, wobei der zumindest eine Reflektionskoeffizient (S11) ein Maß der durch jede Antenne (27; 38; 47; 57; 77, 88) reflektierten Sendeleistung ist, und
- Einstellen der Sendeparameter, basierend auf dem bestimmten Reflektionskoeffizienten (S11), wobei die Sendeparameter Leistungszuteilung unter den Trägern, Strahlformungs-Gewichte, Modulation und/oder Kodierung umfassen.
2. Verfahren nach Anspruch 1, wobei der Reflektionskoeffizient als eine Funktion der
Frequenz bestimmt wird.
3. Verfahren nach Anspruch 2, wobei die zumindest eine Antenne ausgewählt ist, zumindest
eine Sendeantenne (27; 47; 57; 77) zu sein, mit der der Sender (Tx) verbunden ist, wobei der Reflektionskoeffizient für jede Sendeantenne (27; 47; 57;
77) bestimmt wird und das Einstellen der Sendeparameter das Water-Filling über die
zumindest eine Sendeantenne (27; 47; 57; 77) umfasst, um Leistungszuteilung in der
Frequenz zu ermitteln.
4. Verfahren nach einer der Ansprüche 1 - 3, wobei die zumindest eine Antenne ausgewählt
ist, Mehrfach-Sendeantennen (47; 77) zu sein, mit denen der Sender (Tx) verbunden ist, und der Reflektionskoeffizient für jede Sendeantenne (47; 77) als
ein Durchschnittswert über ein Frequenzband bestimmt wird.
5. Verfahren nach Anspruch 4, wobei jede Sendeantenne ein oder mehrere Sendeelemente
(22) aufweist, wobei der Durchschnittswert aus den Reflektionskoeffizienten (S11), die für jedes Antennenelement (22) bestimmt werden, ermittelt wird.
6. Verfahren nach Anspruch 4, wobei der Durchschnittswert für jede Sendeantenne (47)
gemessen wird.
7. Verfahren nach einem der Ansprüche 4 - 6, wobei das Einstellen der Sendeparameter
das Water-Filling über die Sendeantennen (47) umfasst.
8. Verfahren nach einem der Ansprüche 3 - 6, wobei Sende-Auswahl-Diversität verwendet
wird und das Einstellen der Sendeparamenter die Wahl, an welche Sendeantenne (47)
zu senden ist, umfasst.
9. Verfahren nach Anspruch 2, wobei die zumindest eine Antenne ausgewählt ist, zumindest
eine Empfangsantenne (38; 88) in einer Empfangseinheit (42; 92) zu sein, wobei das
Verfahren ferner Folgendes umfasst:
- Bestimmen von zumindest einem Reflektionskoeffizienten (S11) eines schwachen Signals, das an die zumindest eine Empfangsantenne (38; 88) gesendet wird, durch Vergleichen des gesendeten schwachen Signals mit einer Reflektion desselben schwachen Signals in der Empfangseinheit (42; 92),
- Vorhersagen der Kanalzustände von dem Sender zu dem Empfänger, basierend auf dem/den bestimmten Reflektionskoeffizienten in der Empfangseinheit (42; 92), und
- Signalisieren von Informationen bezüglich der Reflektionskoeffizienten zu dem Sender (Tx), um die Sendeparameter einzustellen.
10. Verfahren nach Anspruch 9, wobei die Information bezüglich der Kanalzustände für das
Senden geeignete Frequenzen und/oder für das Senden ungeeignete Frequenzen umfasst.
11. Verfahren nach einem der Ansprüche 9 oder 10, wobei der/die Reflektionskoeffizient(en)
relativ zum schwachen Signal, das in einer Einstelleinheit (31; 81) erzeugt wird,
in der Empfangseinheit (42; 92) bestimmt wird/werden und an die Empfangsantenne (38;
88) gesendet wird/werden.
12. Verfahren nach einem der Ansprüche 9 oder 10, wobei die Empfangseinheit eine Zeitduplex-(TDD)-Einheit
ist, und der/die Reflektionskoeffizient(en) während eines Zeitschlitzes, an den die
TDD-Einheit sendet, bestimmt wird/werden.
13. Verfahren nach einer der Ansprüche 1 - 8, wobei die zumindest eine Antenne ausgewählt
ist, Mehrfach-Sendeantennen (47; 77) zu sein, mit denen der Sender (Tx) verbunden ist, wobei das Verfahren ferner Folgendes umfasst:
- Bestimmen einer zeitlichen Verzögerung, basierend auf der Reflektion des Signals, das von dem Sender (Tx) für jede einzelne Senderkette (481, 482; 781, 782) gesendet wird; und
- Ausgleichen der Unterschiede in der zeitlichen Verzögerung zwischen den einzelnen Senderketten (481, 482; 781, 782), um sicherzustellen, dass das Signal simultan von allen Sendeantennen (47; 77) gesendet wird.
14. Verfahren nach Anspruch 13, wobei die zeitliche Verzögerung für jede einzelne Senderkette
(481, 482; 781, 782) durch Folgendes erzielt wird:
- Messen der Laufzeit in jeder einzelnen Senderkette (481, 482; 781, 782) von dem Antennenanschluss im Sender (Tx) zu jeder Sendeantenne (47; 77), und
- Ermitteln der zeitlichen Verzögerung, um Unterschiede in der zeitlichen Verzögerung zwischen den einzelnen Senderketten (481, 482; 781, 782) auszugleichen.
15. Verfahren nach einem der Ansprüche 1 - 14, wobei das Verfahren ferner das Aktualisieren
des/der gemessenen Reflektionskoeffizienten in regelmäßigen Abständen umfasst.
16. Verfahren nach Anspruch 15, wobei die Aktualisierungsrate höher ist, wenn der Sender
(Tx) und die zumindest eine Antenne in einer mobilen Einheit angeordnet sind, im Vergleich
zu einer Anordnung in einer Basisstation.
17. Verfahren nach Anspruch 16, wobei die Aktualisierungsrate einmal pro Sekunde oder
höher für eine mobile Einheit ist.
18. Knoten, umfassend zumindest eine Antenne, wobei der Knoten konfiguriert ist, zumindest
einen Reflektionskoeffizienten eines Signals für jede Antenne zu bestimmen, wobei
das Signal von einem Sender (Tx) gesendet wird, dadurch gekennzeichnet, das s der Knoten ferner mit einem Mittel (21; 31; 41; 51; 71) zum Einstellen in den Sender
(Tx) ausgestattet ist, basierend auf dem zumindest einen Reflektionskoeffizienten (S11), der durch Vergleichen des gesendeten Signals mit einer Reflektion desselben Signals
bestimmt wird, wobei zumindest ein Reflektionskoeffizient (S11) ein Maß der durch jede Antenne reflektierten Sendeleistung ist, wobei die Sendeparameter
Leistungszuteilung unter den Trägern, Strahlformungs-Gewichte, Modulation und/oder
Kodierung umfassen.
1. Procédé d'adaptation de paramètres d'émission dans un émetteur (Tx) en communication avec au moins une antenne (27 ; 38 ; 47 ; 57 ; 77, 88), ledit procédé
comprenant l'étape ci-dessous consistant à :
- transmettre un signal à partir de l'émetteur (Tx), caractérisé en ce que ledit procédé comporte en outre les étapes ci-dessous consistant à :
- déterminer au moins un coefficient de réflexion (S11) dudit signal pour chaque antenne (27 ; 38 ; 47 ; 57 ; 77, 88) en comparant le signal émis à une réflexion du même signal, lequel au moins un coefficient de réflexion (S11) correspond à une mesure de la puissance émise réfléchie par chaque antenne (27 ; 38 ; 47 ; 57 ; 77, 88) ; et
- adapter les paramètres d'émission sur la base du coefficient de réflexion déterminé (S11), dans lequel les paramètres d'émission comportent une affectation de puissance entre porteuses, des pondérations de conformation de faisceaux, une modulation et/ou un codage.
2. Procédé selon la revendication 1, dans lequel ledit coefficient de réflexion est déterminé
en fonction de la fréquence.
3. Procédé selon la revendication 2, dans lequel ladite au moins une antenne est sélectionnée
comme étant au moins une antenne émettrice (27 ; 47 ; 57 ; 77) à laquelle ledit émetteur
(Tx) est connecté, ledit coefficient de réflexion est déterminé pour chaque antenne émettrice
(27 ; 47 ; 57 ; 77), et l'adaptation de paramètres d'émission comprend une irrigation
à travers ladite au moins une antenne émettrice (27 ; 47 ; 57 ; 77) en vue de calculer
une affectation de puissance en termes de fréquence.
4. Procédé selon l'une quelconque des revendications 1 à 3, dans lequel ladite au moins
une antenne est sélectionnée comme correspondant à de multiples antennes émettrices
(47 ; 77) auxquelles ledit émetteur (Tx) est connecté, et ledit coefficient de réflexion pour chaque antenne émettrice (47
; 77) est déterminé comme étant une valeur moyenne sur une bande de fréquence.
5. Procédé selon la revendication 4, dans lequel chaque antenne émettrice présente un
ou plusieurs éléments d'antenne (22), et la valeur moyenne est calculée à partir des
coefficients de réflexion (S11) déterminés pour chaque élément d'antenne (22).
6. Procédé selon la revendication 4, dans lequel la valeur moyenne est mesurée pour chaque
antenne émettrice (47).
7. Procédé selon l'une quelconque des revendications 4 à 6, dans lequel l'adaptation
de paramètres d'émission comprend une irrigation à travers les antennes émettrices
(47).
8. Procédé selon l'une quelconque des revendications 3 à 6, dans lequel une diversité
de sélection de transmission est utilisée et l'adaptation des paramètres d'émission
consiste à choisir sur quelle antenne émettrice (47) il convient d'émettre.
9. Procédé selon la revendication 2, dans lequel ladite au moins une antenne est sélectionnée
comme étant au moins une antenne réceptrice (38 ; 88) dans une unité de réception
(42 ; 92), ledit procédé comportant en outre les étapes ci-dessous consistant à :
- déterminer au moins un coefficient de réflexion (S11) d'un signal faible transmis à ladite au moins une antenne réceptrice (38 ; 88), en comparant le signal faible émis à une réflexion du même signal faible dans l'unité de réception (42 ; 92) ;
- prédire des états de canal, de l'émetteur au récepteur, sur la base du ou des coefficients de réflexion déterminés dans l'unité de réception (42 ; 92) ; et
- signaler des informations concernant des coefficients de réflexion à l'émetteur (Tx) afin d'adapter les paramètres d'émission.
10. Procédé selon la revendication 9, dans lequel lesdites informations concernant des
états de canal comportent des fréquences appropriées en vue d'une transmission et/ou
des fréquences inappropriées en vue d'une transmission.
11. Procédé selon l'une quelconque des revendications 9 et 10, dans lequel le ou les coefficients
de réflexion est/sont déterminé(s) relativement au signal faible généré dans une unité
d'adaptation (31 ; 81), dans l'unité de réception (42 ; 92), et transmis à l'antenne
réceptrice (38 ; 88).
12. Procédé selon l'une quelconque des revendications 9 ou 10, dans lequel l'unité réceptrice
est une unité de duplexage par répartition dans le temps (TDD), et le ou les coefficients
de réflexion est/sont déterminé(s) au cours d'une tranche de temps dans laquelle l'unité
de duplexage TDD émet.
13. Procédé selon l'une quelconque des revendications 1 à 8, dans lequel ladite au moins
une antenne est sélectionnée comme correspondant à de multiples antennes émettrices
(47 ; 77) auxquelles ledit émetteur (Tx) est connecté, ledit procédé comportant en outre les étapes ci-dessous consistant
à :
- déterminer un retard temporel sur la base d'une réflexion du signal transmis à partir de l'émetteur (Tx) pour chaque chaîne d'émetteurs individuelle (481, 482 ; 781, 782) ; et
- compenser des différences en termes de retard temporel entre les chaînes d'émetteurs individuelles (481, 482 ; 781, 782) en vue de garantir que le signal est transmis simultanément à partir de toutes les antennes émettrices (47 ; 77).
14. Procédé selon la revendication 13, dans lequel le retard temporel pour chaque chaîne
d'émetteurs individuelle (481, 482 ; 781, 782) est obtenu comme suit :
- en mesurant un temps de propagation dans chaque chaîne d'émetteurs individuelle (481, 482 ; 781, 782) depuis un port d'antenne dans l'émetteur (Tx) jusqu'à chaque antenne émettrice (47 ; 77) ; et
- en calculant un retard temporel pour compenser des différences en termes de retard temporel entre les chaînes d'émetteurs individuelles (481, 482 ; 781, 782).
15. Procédé selon l'une quelconque des revendications 1 à 14, dans lequel ledit procédé
comprend en outre une étape de mise à jour du ou des coefficients de réflexion mesurés
à des intervalles réguliers.
16. Procédé selon la revendication 15, dans lequel la fréquence de mise à jour est plus
élevée lorsque ledit émetteur (Tx) et ladite au moins une antenne sont agencés dans une unité mobile que lorsqu'ils
sont agencés dans une station de base.
17. Procédé selon la revendication 16, dans lequel la fréquence de mise à jour correspond
à une mise à jour par seconde, ou plus, pour une unité mobile.
18. Noeud comprenant au moins une antenne, ledit noeud étant configuré de manière à déterminer
au moins un coefficient de réflexion d'un signal pour chaque antenne, ledit signal
étant transmis à partir d'un émetteur (Tx), caractérisé en ce que ledit noeud est en outre doté d'un moyen (21 ; 31 ; 41 ; 51 ; 71) permettant une
adaptation dans ledit émetteur (Tx) sur la base dudit au moins un coefficient de réflexion (S11) déterminé en comparant le signal émis à une réflexion du même signal, lequel au
moins un coefficient de réflexion (S11) correspond à une mesure de la puissance émise réfléchie par chaque antenne, dans
lequel les paramètres d'émission comportent une affectation de puissance entre porteuses,
des pondérations de conformation de faisceaux, une modulation et/ou un codage.